JAVA开发常用类库UUID、Optional、ThreadLocal、TimerTask、Base64使用方法与实例详解

UUID 根据时间戳实现自动无重复字符串定义

// 获取UUID
public static UUID randomUUID()

// 根据字符串获取UUID
public static UUID fromString(String name)

应用：对文件进行自动命名处理

import java.util.UUID;

class Demo {

  public static void main(String[] args) {
    System.out.println(UUID.randomUUID());
    // 85a8ccb1-88f8-4b3c-833d-d45b58e0204e

    System.out.println(UUID.fromString("85a8ccb1-88f8-4b3c-833d-d45b58e0204e"));
    // 85a8ccb1-88f8-4b3c-833d-d45b58e0204e
  }
}

Optional 主要功能是进行null空指针处理

JDK >= 1.8

示例：单独处理null参数

class Message{
  private String message;

  public Message(String message) {
    this.message = message;
  }

  public String getMessage(){
    return this.message;
  }
}

class Demo {
  public static void showMessage(Message message) {
    if(message != null){
      System.out.println(message.getMessage());
    }
  }

  public static void main(String[] args) {
    Message message = new Message("这是消息");
    showMessage(message);

    showMessage(null);
  }
}

几个方法

public final class Optional {

   public static Optional empty() {
    @SuppressWarnings("unchecked")
    Optional t = (Optional) EMPTY;
    return t;
  }

  public static  Optional of(T value) {
    return new Optional<>(value);
  }

   public static  Optional ofNullable(T value) {
    return value == null ? empty() : of(value);
  }

  public T get() {
    if (value == null) {
      throw new NoSuchElementException("No value present");
    }
    return value;
  }

  public T orElse(T other) {
    return value != null ? value : other;
  }
}

使用示例

import java.util.Optional;


Optional optOf = Optional.of("message");
// Optional optOfNull = Optional.of(null);
// java.lang.NullPointerException

Optional optOfNullable = Optional.ofNullable("message");
Optional optOfNullableNull = Optional.ofNullable(null);



System.out.println(optOf.get());
// message

System.out.println(optOfNullable.get());
// message

// System.out.println(optOfNullableNull.get());
// java.util.NoSuchElementException: No value present

System.out.println(optOf.orElse("default"));
// message

System.out.println(optOfNullable.orElse("default"));
// message

System.out.println(optOfNullableNull.orElse("default"));
// default

自定义函数实现

class Demo {
  public static String getDefault(String object, String defaultValue){
    return object != null ? object : defaultValue;
  }

  public static void main(String[] args) {
    System.out.println(getDefault("message", "default"));
    // message

    System.out.println(getDefault(null, "default"));
    // default
  }
}

ThreadLocal解决线程同步问题

public T get() 
public void set(T value)
public void remove()

定义发送消息类

class Message{
  private String message ;

  public Message(String message) {
    this.message = message;
  }

  public String getMessage(){
    return this.message;
  }
}

class Channel{
  private static Message message;

  public static void setMessage(Message msg){
    message = msg;
  }

  public static void send(){
    System.out.println(message.getMessage());
  }

}

单线程下运行

class Demo {
  public static void main(String[] args) {
    Message message = new Message("你好");
    Chanel.setMessage(message);
    Chanel.send();
    // 你好
  }
}

多线程下运行，出现数据覆盖现象

class Demo {
  public static void main(String[] args) {
    new Thread(()->{
      Channel.setMessage(new Message("你好-1"));
      Channel.send();
    }, "线程-1").start();

    new Thread(()->{
      Channel.setMessage(new Message("你好-2"));
      Channel.send();
    }, "线程-2").start();

    new Thread(()->{
      Channel.setMessage(new Message("你好-3"));
      Channel.send();
    }, "线程-3").start();
    
  }
}

改造 Channel

class Channel{

  // private static Message message;
  private static final ThreadLocal THREAD_LOCAL = new ThreadLocal();

  public static void setMessage(Message msg){
    THREAD_LOCAL.set(msg);
  }

  public static void send(){
    System.out.println(Thread.currentThread().getName()
 + " "
 + THREAD_LOCAL.get().getMessage());
  }  
}

// 执行后数据对应

ThreadLocal， 只允许保存一个数据

定时器进行定时任务处理，实现了一种间隔触发操作

java.util.TimerTask 定时任务处理

java.util.Timer 任务启动

// 定时启动
public void schedule(TimerTask task, long delay)

// 间隔任务
public void scheduleAtFixedRate(TimerTask task, long delay, long period)

定义任务

import java.util.TimerTask;

class MyTask extends TimerTask{

  @Override
  public void run() {
    System.out.println("任务启动 " + System.currentTimeMillis());
  }
}

示例：定时启动，会卡主

import java.util.Timer;

class Demo {
  public static void main(String[] args) {
    Timer timer = new Timer();
    timer.schedule(new MyTask(), 100);
    // 任务启动 1574260837613
  }
}

示例：间隔任务

class Demo {
  public static void main(String[] args) {
    Timer timer = new Timer();
    timer.scheduleAtFixedRate(new MyTask(), 100, 1000);
  }
}

加密解密示例

String message = "Hello Java";

String encodeMessage = new String(base64.getEncoder().encode(message.getBytes()));

System.out.println(encodeMessage);

// SGVsbG8gSmF2YQ==

String decodeMessage = new String(base64.getDecoder().decode(encodeMessage));

System.out.println(decodeMessage);

// Hello Java

最好的方法是使用2-3中加密程序，进行多次加密

加密解密示例

import java.util.base64;

class Crypto{
  // 加密重复次数，越高越安全
  private static final int REPEAT = 3;

  
  public static String encode(String message){
    byte[] data = message.getBytes();

    // 重复加密
    for (int i = 0; i < REPEAT; i++) {
      data = base64.getEncoder().encode(data);
    }

    return new String(data);
  }

  public static String decode(String message){
    byte[] data = message.getBytes();

    for (int i = 0; i < REPEAT; i++) {
      data = base64.getDecoder().decode(data);
    }

    return new String(data);
  }
}

class Demo {
  public static void main(String[] args) {
    String message = "Hello Java";

    String encodeMessage = Crypto.encode(message);
    System.out.println(encodeMessage);
    // VTBkV2MySkhPR2RUYlVZeVdWRTlQUT09

    String decodeMessage = Crypto.decode(encodeMessage);
    System.out.println(decodeMessage);
    // Hello Java
  }
}

本文主要介绍了JAVA开发过程中常用类库UUID、Optional、ThreadLocal、TimerTask、base64的基础使用方法，更多关于UUID、Optional、ThreadLocal、TimerTask、base64类库的详细使用方法请查看下面的相关链接